Electrochromic media with concentration-enhanced stability, process for the preparation thereof and use in electrochromic devices

Abstract

Increased stability of electrochromic devices containing an electrochromic medium having two or more electroactive compounds is accomplished by establishing current limiting concentrations of electroactive compounds with the larger redox potential difference. A process for production of electrochromic devices uses targeted concentrations of electroactive materials during preparation of the electrochromic medium which results in substantially no devices being produced wherein the current is limited by an electroactive compound having a low redox potential difference.

What is claimed is: 
     
       1. An electrochromic medium, comprising: a) a solvent   b) an anodic electroactive material which exhibits at least two chemically reversible waves in a cyclic voltammogram in said solvent at room temperature,   c) a cathodic electroactive material which exhibits at least two chemically reversible waves in a cyclic voltammogram in said solvent at room temperature;   wherein at least one of said electroactive materials is electrochromic, and wherein the electroactive material having the smaller potential difference between the chemically reversible waves has a concentration in the electrochromic medium greater than that required to achieve a balanced concentration.   
     
     
       2. The electrochromic medium of claim 1, comprising two electroactive materials, both of which are electrochromic. 
     
     
       3. The electrochromic medium of claim 1, comprising at least three electroactive materials, at least two of which are electrochromic. 
     
     
       4. The electrochromic medium of claim 3, wherein at least three electrochromic materials are present. 
     
     
       5. The electrochromic medium of claim 1, wherein said solvent is contained in a gel or a swellable polymer. 
     
     
       6. The electrochromic medium of claim 1, wherein said anodic electroactive materials are 5,10-dihydrophenazines. 
     
     
       7. The electrochromic medium of claim 1, wherein said cathodic electroactive materials are bipyridinium salts. 
     
     
       8. The electrochromic medium of claim 1, wherein said electroactive material having the smaller potential difference between the chemically reversible waves has a concentration in the electrochromic medium which is greater by 3 equivalent percent or more over the balanced concentration. 
     
     
       9. The electrochromic medium of claim 1, wherein said electroactive material having the smaller potential difference between the chemically reversible waves has a concentration in the electrochromic medium which is greater by 5 equivalent percent or more over the balanced concentration. 
     
     
       10. An electrochromic medium comprising a) an anodic electroactive material,   b) a cathodic electroactive material,   wherein at least one of said electroactive materials is electrochromic,   wherein one of said electroactive materials has only one electrochemically activated state, and wherein a second electroactive material has at least two chemically electrochemically activated states, and wherein the electroactive material with at least two electrochemically activated states has a concentration in the electrochromic medium greater than that required to achieve a balanced concentration.   
     
     
       11. The electrochromic medium of claim 10, wherein said electrochemical medium comprises at least one electroactive material having at least two chemically reversible waves in a cyclic voltammogram. 
     
     
       12. The electrochromic medium of claim 10, wherein said electroactive material with at least two activated states is present in said electrochromic medium in a concentration which is greater by 3 equivalent percent or more over the balanced concentration. 
     
     
       13. The electrochromic medium of claim 10, wherein said electroactive material with at least two activated states is present in said electrochromic medium in a concentration which is greater by 5 equivalent percent or more over the balanced concentration. 
     
     
       14. An electrochromic medium, comprising: a) an anodic electroactive material,   b) a cathodic electroactive material,   wherein one of said anodic electroactive material(s) and said cathodic electroactive material(s) has an electrochemically activated state which exhibits greater reactivity than the electrochemically activated state of other of said electroactive materials, wherein the electroactive material exhibiting said greater reactivity is present in concentration greater than that required to achieve a balanced concentration.   
     
     
       15. The electrochromic medium of claim 14, wherein said anodic electroactive material has an electrochemically activated state which exhibits the greater reactivity, and said anodic electroactive material is present in a concentration greater than that required to achieve a balanced concentration. 
     
     
       16. The electrochromic medium of claim 14, wherein said cathodic electroactive material has an electrochemically activated state which exhibits the greater reactivity, and said cathodic electroactive material is present in a concentration greater than that required to achieve a balanced concentration. 
     
     
       17. The electrochromic medium of claim 14, wherein said electroactive material which exhibits greater reactivity is present in a concentration of 3 equivalent percent or more greater than the balanced concentration. 
     
     
       18. The electrochromic medium of claim 14, wherein said electroactive material which exhibits greater reactivity is present in a concentration of 5 equivalent percent or more greater than the balanced concentration. 
     
     
       19. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 1. 
     
     
       20. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 2. 
     
     
       21. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 3. 
     
     
       22. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 4. 
     
     
       23. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 10. 
     
     
       24. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 11. 
     
     
       25. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 14. 
     
     
       26. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 15. 
     
     
       27. An electrochromic device comprising front and rear spaced elements each having front and rear surfaces, said rear surface of said front element having a transparent conductive material disposed thereon, said front surface of said rear element having a conductive material disposed thereon or said rear element itself being conductive, wherein said front and rear elements are sealably bonded together in a spaced apart relationship to define a cavity, where said cavity contains the electrochromic medium of claim 16. 
     
     
       28. The electrochromic device of claim 19, wherein said device is an electrochromic mirror. 
     
     
       29. The electrochromic device of claim 20, wherein said device is an electrochromic mirror. 
     
     
       30. The electrochromic device of claim 21, wherein said device is an electrochromic mirror. 
     
     
       31. The electrochromic device of claim 22, wherein said device is an electrochromic mirror. 
     
     
       32. The electrochromic device of claim 23, wherein said device is an electrochromic mirror. 
     
     
       33. The electrochromic device of claim 24, wherein said device is an electrochromic mirror. 
     
     
       34. The electrochromic device of claim 25, wherein said device is an electrochromic mirror. 
     
     
       35. The electrochromic device of claim 26, wherein said device is an electrochromic mirror. 
     
     
       36. The electrochromic device of claim 27, wherein said device is an electrochromic mirror. 
     
     
       37. A process for the preparation of an electrochromic device wherein an electrochromic medium is introduced into a cavity in said device, said electrochromic medium containing at least one anodic electroactive compound and at least one cathodic electroactive compound, at least one of said electroactive compounds being an electrochromic compound, the improvement comprising: adjusting the concentrations of said electroactive compounds to establish an increased relative concentration of the electroactive material having the smaller redox potential difference such that said increased concentration is greater than that required to achieve a balanced concentration.   
     
     
       38. The process of claim 37, wherein said increased concentration is sufficient to substantially eliminate production of devices having the electroactive material having the smaller redox potential difference as the current limiting species or less than that required to achieve a balanced concentration due to variations in measuring the relative amounts of electroactive compounds when preparing said electrochromic medium. 
     
     
       39. The process of claim 37, wherein at least one anodic electroactive compound (A 1 ) which exhibits two chemically reversible waves in a cyclic voltammogram is present and at least one cathodic electroactive compound (C 1 ) which exhibits two chemically reversible waves is present, the electroactive compound (A 1 ) or (C 1 ) having the largest redox potential difference being present in a concentration less than that required to achieve a balanced concentration. 
     
     
       40. The process of claim 37, wherein at least one anodic electroactive compound (A 1 ) which exhibits two chemically reversible waves in a cyclic voltammogram is present and at least one cathodic electroactive compound (C 1 ) which exhibits two chemically reversible waves is present, the electroactive compound (A 1 ) or (C 1 ) having the smallest redox potential difference being present in a concentration greater than that required to achieve a balanced concentration. 
     
     
       41. The process of claim 37, wherein one of said electroactive materials is an anodic electroactive compound (A 1 ) or a cathodic electroactive compound (C 1 ) which exhibits two chemically reversible waves in a cyclic voltammogram, and one of said electroactive materials is an electroactive compound (A 2 ) which exhibits only one electrochemically activated state, or a cathodic electroactive compound (C 2 ) which exhibits only one electrochemically activated state, wherein said electroactive compound (A 2 ) or (C 2 ) is present in a concentration less than that required to achieve a balanced concentration. 
     
     
       42. The process of claim 37, wherein at least one of said electroactive materials exhibits an electrochemically activated state which is less chemically stable than the electrochemically activated states of other electroactive materials in said electrochromic medium, said electroactive material which exhibits said less chemically stable electrochemically activated state being present in a concentration greater than that required to achieve a balanced concentration.